LAUSR

Background and objective: Invasive micropapillary carcinoma (IMPC) of the breast is a special variant of breast carcinoma with a unique morphology. Data about long-term outcome are conflicting and reports on stromal tumor infiltrating lymphocytes (sTILs) and their correlation with prognosis are scarce. In this retrospective cohort study we aimed to describe clinical and pathological features of IMPC, including sTILs assessment and immunohistochemistry studies, and their correlation with long-term outcome. Materials and methods: Patients with stage I-III IMPC (pure and mixed forms) who underwent upfront surgery at our institution between 2000 and 2016 were included. All patients signed informed consent. Standard clinico-pathological features and follow-up data to calculate distant relapse-free interval and breast cancer-specific survival were obtained from clinical records. Pathologic review of representative HE range 33-88). Luminal surrogate subtypes were most prevalent with 51 luminal A-like, 41 luminal B-like, 12 luminal HER2+, 5 HER2+ and 2 triple negative IMPC. 89% of patients had a T1 or T2 tumor and 50% of IMPC were poorly differentiated. Lymph node involvement was present in 59% and lymphovascular invasion in 44% of cases. Adjuvant chemotherapy, radiotherapy and endocrine therapy was administered in 47%, 87% and 90% of patients, respectively. Of all cases 59% were pure IMPC. Standard clinico-pathological features were comparable between pure and non-pure IMPC. sTILs were classified as low ( 50%) in 78%, 14% and 8% of specimens respectively. Comparison between surrogate subtypes showed higher sTILs (p=0.025) and a higher likelihood of aberrant P53 expression (p Citation Format: Kevin Punie, Frederik Deman, Annouschka Laenen, Timothy Faes, Hans Wildiers, Ann Smeets, Ines Nevelsteen, Chantal Van Ongeval, Adinda Baten, Melissa Christiaens, Eva Oldenburger, Hilde Janssen, Caroline Weltens, Tatjana Geukens, Nynke Willers, Jan Ardui, Hava Izci, Laurence Slembrouck, Patrick Neven, Christine Desmedt, Giuseppe Floris. Clinical and pathological features of invasive micropapillary carcinoma of the breast and correlation with prognosis [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-08-31.